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Schooling · Class 10 · Science · The Human Eye and the Colourful World · Chapter on a page

CBSE Class 10 · Science · NCERT Science

The Human Eye and the Colourful World: chapter on a page

A cut of Shishya's notes for this chapter: the first paragraph of the introduction and the key ideas, formulas and facts, common mistakes and quick revision lists, word for word. Nothing is added or reworded; the worked examples are left out (they are on the chapter page).

About the notes: Written by Shishya's AI on 26 Sept 2026 from the chapter's title and class level, in Shishya's own words — not a copy or summary of the textbook. Read the official chapter for the book's own text, activities and exercises.

This note's current text has no applied fact-check on record.

Mind map

Drawn from the same notes by a fixed rule (no AI): each label is the item's own words — its bold term, its label before a colon, a short formula as written, or its first words.

Mind map of The Human Eye and the Colourful World: Key ideas, Formulas and facts, Watch out forKey ideasThe human eye uses a convex lens to…The ciliary muscles change the…The least distance of distinct…Myopia (short-sightedness) occurs…Hypermetropia (long-sightedness)…White light splits into seven…Scattering of light by atmospheric…Formulas and factsP = 1/fFor myopia correctionFor hypermetropia correctionThe angle of deviation in a prism is…The order of colours in the visible…Shorter wavelengths (blue, violet)…The near point of a young person…Watch out forThinking that a convex lens corrects…Confusing near point and far pointBelieving the sky is blue because of…Forgetting to use correct sign…Thinking stars twinkle because they…The Human Eye andthe Colourful World
The mind map as a list
  • Key ideas
    • The human eye uses a convex lens to…
    • The ciliary muscles change the…
    • The least distance of distinct…
    • Myopia (short-sightedness) occurs…
    • Hypermetropia (long-sightedness)…
    • White light splits into seven…
    • Scattering of light by atmospheric…
  • Formulas and facts
    • P = 1/f
    • For myopia correction
    • For hypermetropia correction
    • The angle of deviation in a prism is…
    • The order of colours in the visible…
    • Shorter wavelengths (blue, violet)…
    • The near point of a young person…
  • Watch out for
    • Thinking that a convex lens corrects…
    • Confusing near point and far point
    • Believing the sky is blue because of…
    • Forgetting to use correct sign…
    • Thinking stars twinkle because they…

What this chapter is about

This chapter explains how the human eye works as an optical device. You will learn about the structure of the eye, how it forms images, and how it adjusts to see objects at different distances. The chapter builds on your understanding of lenses from earlier work on light and refraction.

Key ideas

  • The human eye uses a convex lens to form a real, inverted image on the retina. The brain interprets this image as upright.
  • The ciliary muscles change the curvature of the eye lens to adjust its focal length, allowing the eye to focus on near and distant objects. This ability is called accommodation.
  • The least distance of distinct vision for a normal eye is about 25 cm. The far point for a normal eye is at infinity.
  • Myopia (short-sightedness) occurs when the image forms in front of the retina. It is corrected using a concave lens.
  • Hypermetropia (long-sightedness) occurs when the image forms behind the retina. It is corrected using a convex lens.
  • White light splits into seven colours (VIBGYOR) when passing through a prism because different colours have different speeds in glass. This is called dispersion.
  • Scattering of light by atmospheric particles causes the blue colour of the sky and the reddish appearance of the sun at sunrise and sunset.
  • Atmospheric refraction causes the twinkling of stars and the apparent shift in positions of celestial objects.

Formulas and facts to remember

  • Power of a lens: P = 1/f, where f is the focal length in metres and P is in dioptres (D).
  • For myopia correction: A concave lens of focal length equal to the defective far point distance is needed.
  • For hypermetropia correction: A convex lens is needed so that the near point shifts to 25 cm.
  • The angle of deviation in a prism is smallest for yellow-green light and greatest for violet light.
  • The order of colours in the visible spectrum by decreasing wavelength: Red, Orange, Yellow, Green, Blue, Indigo, Violet (VIBGYOR when reversed).
  • Shorter wavelengths (blue, violet) scatter more than longer wavelengths (red, orange). This is Rayleigh scattering.
  • The near point of a young person with normal vision is about 25 cm; for an elderly person, it may be much farther.

Common mistakes

  • Thinking that a convex lens corrects myopia → Myopia needs a concave lens because the image forms too early; diverging rays push the image back to the retina.
  • Confusing near point and far point → Near point is the closest distance for clear vision (25 cm normally); far point is the farthest distance (infinity normally).
  • Believing the sky is blue because of reflection from oceans → The blue colour is due to scattering of shorter wavelengths by atmospheric molecules, not reflection.
  • Forgetting to use correct sign conventions in lens calculations → Always treat distances on the object side as negative and apply the lens formula consistently.
  • Thinking stars twinkle because they emit unsteady light → Twinkling is caused by changing atmospheric refraction, not by changes in the star itself.

Quick revision

  • The eye lens changes shape to focus; this is accommodation.
  • Myopia: image before retina; correct with concave lens.
  • Hypermetropia: image behind retina; correct with convex lens.
  • Dispersion splits white light because different colours have different speeds in glass.
  • Blue sky: blue light scatters more. Red sunrise/sunset: blue scatters away, red reaches us.
  • Power of lens in dioptres = 1 ÷ focal length in metres.